Colloidal processing, surface characterization, and sintering of nano ZrO2 powders

Colloidally stable suspensions are required to fabricate dense samples with uniform microstructure by colloidal processing methods, which necessitate dispersion of ceramic powders in a liquid medium. Aqueous nano ZrO2 suspensions were prepared using polyethylenimine (PEI) as a dispersant. PEI adsorption on nano ZrO2 surfaces was promoted with increasing initial PEI content and suspension pH. Isoelectric point was shifted from pH 7 at 0 wt% PEI to pH 10.4 at 3 wt% PEI. Stable suspensions had mean particle sizes in the range of 100 to 150 nm and sedimentation rates less than 0.4 mm/h, as compared to 2-5.5 mu m and 10-50 mm/h for unstable suspensions. Samples with 98% relative density were fabricated after sintering at 1300 degrees C for 4 h from colloidally stable suspensions.